That depends on whether it's a celebration of moving forward with your life or a celebration of getting rid of 'him', which I agree would be quite nasty. Many of us have rituals of some sort throughout our life dividing up 'then' and 'now' - graduation, marriage, various birthdays, etc. Although I can't say I had many of them.
I assume your son isn't invited! Maybe he ought to have his own celebration - a private party with his family or friends, a day out on his own to somewhere he's always wanted to go. A celebration doesn't have to be a drunken 'whoopee' affair, just something that allows you to say 'that's the past, now let's move forward' to something better'.